Loss of alertness has been blamed for a large percentage of all road crashes. For example, loss of alertness is believed to cause up to twenty percent of all traffic accidents in Europe. In the U.S., falling asleep at the wheel is believed to cause at least 100,000 crashes annually. As many as twenty eight percent of polled American drivers have admitted to nodding off at the wheel at least once.
Various techniques have been studied to monitor a driver's driving performance and predict loss of alertness. Such techniques typically rely upon monitoring lane departure, large lateral deviations within a lane, cessation of steering corrections, and/or many other metrics of driving performance. However, no consensus is known regarding which metric or a combination of metrics is a more reliable indicator of driver alertness than other metrics.